1. Field of the Invention
The present invention relates to a urethane foam molded article used as, for example, an acoustic material or a vibration absorber, a manufacturing method thereof, and a magnetic induction foam molding apparatus suitable for the manufacturing of the urethane foam molded article.
2. Description of the Related Art
The urethane foam molded article is frequently used as a cushion material, an acoustic material, a vibration absorber etc. in various fields such as articles for daily use, automobile, architecture. The urethane foam molded article is usually produced by foam-molding a liquid urethane foam resin raw material in a cavity of a foaming mold (for example, see Japanese Patent Application Publication Nos. 2003-97645, 2005-48023). On the other hand, for eliminating a defect such as an underfill of the urethane foam molded article, Japanese Patent Application Publication No. 2006-181777 disclose a method in which magnetic bodies are blended in a urethane foam resin raw material and a resultant raw material is subjected to foam molding while attracting the magnet body by applying a magnetic field from one direction. In addition, it is not the foam molding, however, as a method for imparting electric conductivity or thermal conductivity to a resin molded article, a method in which powder of metal magnetic bodies is kneaded with a resin and the resin is molded in a magnetic field, is disclosed (for example, see Japanese Patent Application Publication No. 2002-11758).
However, in a conventional molding method utilizing the magnetic field, the distribution of the magnetic force in the cavity of the foaming mold etc. is not taken into consideration. For example, when the molding is performed between the magnets opposed to each other, the closer to the outer circumference of the magnet, the more the lines of magnetic force fleeing outward. Therefore, along the direction of a diameter expansion of the magnet, the magnetic flux density becomes smaller. In addition, when the distance between the magnets becomes larger, according to the distance to a magnet, the difference in the magnetic flux density is likely to be caused. Therefore, it is difficult to apply a uniform magnetic field to the whole of the molding material filled in the cavity. When a molding material to which magnetic bodies are blended is molded in a magnetic field, the magnetic bodies are oriented along the lines of magnetic force. Accordingly, in a magnetic field in which the lines of magnetic force are not uniform and the difference in the magnetic flux density is large, a molded article in which the magnetic bodies are eccentrically-located according to the magnetic flux density is produced.
Accordingly, when the foam molding is performed in a magnetic field in which the magnetic flux density is not uniform and a field gradient is present, the magnetic bodies in a urethane foam resin raw material are moved in an unnecessary direction along the lines of magnetic force, so that a desired oriented state cannot be obtained. Therefore, in a produced urethane foam molded article, desired properties are difficulty obtained. In this case, for example, by increasing the blended amount of the magnetic bodies, the dispersibility of the magnetic bodies can be enhanced. However, the influence on the foam molding becomes larger by the increment of the blended amount of the magnetic bodies. As the result, there is such a fear that various characteristics such as sound absorbing characteristics, heat insulating property and cushion property are lowered. In addition, the weight of the urethane foam molded article is increased, and the manufacturing cost also becomes large.